1. Field of the Invention
The present invention relates to a variable valve timing controller for an internal combustion engine, which has a camshaft and a crankshaft. The variable valve timing controller has an intermediate lock mechanism that locks a rotational phase (variable cam timing phase) of the camshaft relative to the crankshaft at an intermediate lock position.
2. Description of Related Art
As described in JP-A-H9-324613 (corresponding to U.S. Pat. No. 5,738,056) or JP-A-2001-159330 (corresponding to U.S. Pat. No. 6,330,870), during the stop of the engine, a conventional hydraulic variable valve timing unit is configured to set a lock position at a generally middle of an adjustable range of the variable cam timing (VCT) phase. Thus, it is possible to enlarge the adjustable range of the valve timing (VCT phase). In the above configuration, an intermediate lock position, at which the VCT phase is locked during the stop of the engine, is determined to be suitable for the start of the engine. Thus, the engine is started under a state, where the VCT phase is at the intermediate lock position. Then, when oil pressure has been increased to an appropriate oil pressure due to engine rotation increase (oil pump rotation increase) after the start of the engine has been completed, the lock of the VCT phase is released such that the VCT phase is feed-back controlled to a target phase that is determined in accordance with an engine operational state. Then, when a lock request is generated for stopping the engine or during a stand-by operation, a lock control is executed to lock the VCT phase at the intermediate lock position.
However, in a hydraulic control valve having a certain configuration, it is disadvantageously difficult to achieve both of (a) accuracy and reliability of the phase control and (b) high responsivity in a lock pin control (lock operation and lock release operation).